This invention relates to optical switches and in particular, to optical cross-bar switches.
When two parties communicate over a telephone network, a single physical communication path is set up between their two telephones. Given the vast number of telephones, it is impractical to actually wire each telephone to all other telephones on the telephone network. Instead, the telephones are connected to switches. These switches cooperate to establish and tear down physical paths between telephones on an as-needed basis.
In the early days of telephony, the xe2x80x9cswitchxe2x80x9d was a human operator who sat in front of a switchboard making connections between pairs of receptacles, each receptacle corresponding to a telephone line. Because the telephone signals were electrical signals traveling on copper wire, the operator would connect the two receptacles with a length of copper wire, just like the copper wire on which the telephone signals traveled. Eventually, the operator gave way to automated electromechanical, and later to all electronic switching devices. The connection between the two telephone lines, however, remained electrical. This was reasonable because the telephone signals themselves continued to travel as electrical signals on copper wire.
The end of the last century saw the advent of telephone signals propagating as beams of light on optical fibers rather then as electrical signals on copper wires. Nevertheless, the switches that connected optical fibers together remained electrical. As a result, an optical signal propagating on the optical fiber would have to be converted to an electrical signal, switched, and then converted back to an optical signal.
The need to convert between optical signals and electrical signals is a significant bottleneck in a network having fiber-optic communication paths. A conventional fiberoptic cable can easily carry 15,000 Gbps. The currently practical limit of 40 Gbps is primarily the result of a limit at which currently available optoelectronic devices can switch between optical and electrical signals. It is therefore desirable to replace optoelectronic switches with all-optical switches.
The invention provides an optical switching element for use in an optical cross-bar array. The optical switching element includes a magnetically responsive curtain that switches between an extended state and a deflected state in response to an applied switching-field.
A switching element that operates in the foregoing manner includes a curtain that moves in response to a magnetic field. The curtain has a fixed edge attached to a substrate and a free edge opposite the fixed edge. A first magnetic-field source magnetically coupled to the curtain generates a first magnetic field that urges the curtain into an extended position in which the curtain intercepts the optical beam. A second magnetic-field source, also magnetically coupled to the curtain, generates a second magnetic field that urges the curtain into a deflected position in which the curtain avoids intercepting the optical beam.
The default state of the curtain can be either the extended state or the deflected state. In the latter case, the first magnetic-field source includes an electromagnet, and the second magnetic-field source includes a permanent magnet. In the former case, the first magnetic-field source includes a permanent magnet, and the second magnetic-field source includes an electromagnet.
The electromagnet can be one or more coils disposed proximate to the free edge of the curtain. In one aspect of the invention, electromagnet includes a first coil proximate to a first face of the curtain. In another aspect of the invention, the electromagnet further includes a second coil proximate to a second face of the curtain. This second coil can be directly opposed to the first coil or diagonally opposed to the first coil.
The curtain itself can include a pre-stressed portion having a tendency to urge the curtain into a position selected from the extended position and the deflected position. The pre-stressed portion can include the entire curtain, a bottom region of the curtain adjacent to the free edge of the curtain, or a corner of the curtain.
In another aspect of the invention, the switching element forms a bistable switch. In one embodiment of such a bistable switch, the switching element includes third and fourth magnetic-field sources magnetically coupled to the curtain. The third magnetic-field source generates a switching field that switches the curtain from the deflected state to the extended state. The fourth magnetic-field source generates another switching field that urges the curtain from the extended state to the deflected state.
In one particular embodiment, the apparatus includes a first member having a first planar surface and a second member having a second planar surface opposed to the first planar surface, the first and second planar surfaces being separated by a gap. A curtain hinged to the first member extends toward the second surface across the gap. This curtain has two positions: an extended position in which the curtain intercepts an optical beam and a deflected position in which the curtain avoids the optical beam. The curtain is held in one of the two positions by a biasing field and switched to the other position by a switching field generated by an electromagnet.
The invention also includes an optical switch of switching elements for coupling an optical beam from a selected input fiber to a selected output fiber. The optical switch includes an array of switching elements arranged into rows and columns on a substrate. Each row corresponds to an output fiber and each column corresponds to an input fiber.
Each of the switching elements includes a curtain that moves in response to a magnetic field. The curtain has a fixed edge attached to the substrate and a free edge opposite the fixed edge. Each switching element also includes first and second magnetic field sources magnetically coupled to the curtain. One of these magnetic-field sources generates a magnetic field that urges the curtain into an extended position in which the curtain intercepts the optical beam. The other magnetic-field source generates a second magnetic field that urges the curtain into a deflected position in which the curtain avoids intercepting the optical beam.
These and other features of the invention will be apparent from the following detailed description and the accompanying figures, in which: